Anal fistula surgery

Expert reviewer, Mrs Sara Badvie, Consultant Laparoscopic, Colorectal and General Surgeon
Next review due, October 2022

An anal fistula is a small tunnel that develops between the skin around your anus and the very end of your back passage (the anal canal). You’ll usually need to have surgery to treat an anal fistula.

Image showing the large and small bowels

About anal fistula

An anal fistula can develop if you’ve had an infection affecting the glands around your anus. The infection can cause an abscess (a collection of pus) between your skin and anus. When the pus drains away, it may leave a small tunnel (the fistula) behind.

Around a third of people with an abscess in their anus go on to develop a fistula. They can also be caused by long-term bowel conditions, such as Crohn’s disease.

A fistula is usually a simple tunnel between your skin and your anal canal. However, sometimes additional tracts can develop from the same tunnel, or it can pass through the muscles of your anus (your sphincter muscles). These are known as complex anal fistulas and can be more difficult to treat.

You'll usually need to have surgery if you have an anal fistula – they don’t usually heal by themselves, and without treatment, they can lead to repeated abscesses.

Symptoms of anal fistula

Symptoms of an anal fistula can include:

  • discharge coming from the opening of the fistula in your skin, which you may feel as a hole or lump – this may have pus or blood in it
  • pain, discomfort and swelling in and around your anus
  • diarrhoea
  • irritated skin around your anus

These symptoms aren't always caused by an anal fistula, but if you have them, see your GP.

Diagnosis of anal fistula

Your GP will ask about your symptoms and may examine you. Your GP may be able to see the opening of an anal fistula in the skin around your anus (known as the external opening). They may check for further signs by gently inserting their finger inside your back passage. Your GP may refer you to a colorectal surgeon for further investigation and treatment.

Your surgeon may need to do some additional tests and examinations if the diagnosis isn’t clear, or if you have a complex fistula with multiple tracts.

These may include an ultrasound scan of your anus, using a probe inserted into your back passage, a magnetic resonance imaging (MRI) or a computer tomography (CT) scan. They may also do a more detailed physical examination of your anus under anaesthesia if necessary.

About anal fistula surgery

There are various different types of surgery for anal fistula – see the 'What happens during surgery' section below for full details. All types of surgery for anal fistula aim to get rid of the fistula, while causing as little damage to the sphincter muscles around your anus as possible. These muscles allow you to control when you open your bowels – so damage to them can result in a loss of control (incontinence).

After assessing you, your surgeon will talk to you about the different choices that may be available, the risks and benefits and what they recommend for you. This will depend on where exactly your fistula is and whether it involves any of the sphincter muscle.

Your surgeon will explain exactly what will happen during the procedure, what to expect afterwards and the risk of potential complications. Be sure to ask any questions you have, and ask for more time to make a decision if you need it. If you’re happy to go ahead with the procedure, you’ll be asked to sign a consent form – so it’s important to make sure you feel properly informed.

Preparing for anal fistula surgery

Your surgeon will explain how to prepare for your anal fistula surgery. For example, if you smoke, you’ll be asked to stop, as smoking increases your risk of getting a wound or chest infection, and slows wound healing.

Your operation will usually be done under general anaesthesia which means you’ll be asleep during the operation. Some procedures for anal fistula can also be done using regional anaesthesia. This means you’ll be awake during the operation, but the lower part of your body will be numb. After your operation, you’ll usually be able to go home the same day. You’ll need someone who can drive you home and stay with you overnight.

If you’re having a general anaesthetic, you’ll need to stop eating and drinking a few hours before your procedure. Follow your anaesthetist/doctor's advice and if you have any questions, just ask.

On the day of your procedure, your surgeon will meet with you to check you are well and still happy to go ahead. The staff at the hospital will do any final checks and get you ready for surgery. This may include asking you to wear compression stockings, or having an injection of an anticlotting medicine to help prevent deep vein thrombosis (DVT).

What happens during anal fistula surgery?


The most common type of operation for simple fistulas is a fistulotomy. This involves opening up the fistula so that it can heal from the inside out. Once your anaesthetic has taken effect, your surgeon will insert a probe into the opening of the fistula. They’ll then cut through the skin and underlying tissues, opening up the top of the fistula. The wound is left open without any stitches so that it can gradually heal. This type of operation works well for the majority of simple fistulas.

Other options for complex fistulas

Occasionally you may need a different type of treatment. This is more likely if your fistula passes through more of your sphincter muscle, you have several fistulas, or if your fistula keeps coming back.

Your surgeon may initially pass a small thread, called a seton, through your fistula before any other procedure. This helps to drain it to prevent infection. Some people just continue to have treatment with setons over the long term, without going on to have any further procedures.

Other types of surgery include the following.

  • Staged fistulotomy. This is when you have several operations over a number of months, to open up the fistula a little at a time. A loose seton is placed around the remaining fistula each time until your next operation, to help drain it.
  • A cutting seton. This is a specific type of seton that gradually cuts through the sphincter muscle, opening up the fistula and allowing scar tissue to form behind. This reduces the risk of incontinence.
  • Anal advancement flaps. This involves creating a ‘flap’ of tissue within your anal canal, which is sewn down over the fistula opening. It avoids your surgeon needing to cut through your sphincter muscle.
  • Plugs, glues and pastes. These can be inserted or injected into your fistula to block it and help it to heal. There isn’t much good evidence to show that these work – but they give another option that avoids cutting your sphincter muscle. Your doctor may recommend trying it as part of a research trial.
  • LIFT procedure (ligation of the intersphincteric fistula tract). This surgery is for fistulas that pass through the sphincter muscles. It involves closing up one end of the fistula before cutting the fistula open, between your sphincter muscles.
  • Endoscopic ablation. This procedure involves using an electrode to burn away tissue inside the fistula, before sealing it up.
  • Laser therapy. In this procedure, laser therapy is used to destroy and seal the fistula. There’s limited evidence on how well it works. Not all surgeons provide this, and it can only be done in certain circumstances.

What to expect afterwards

You’ll need to rest until the effects of the anaesthetic have passed. You’re likely to have some discomfort as the anaesthetic wears off, but you'll be offered pain relief as you need it. If you have any problems passing urine after your surgery, you may need a catheter at first (a tube that drains urine from your bladder).

Once you’re ready, your nurses will encourage you to get up and move around. This will help to prevent complications. You can begin to drink and eat when you feel ready.

You’ll usually be able to go home on the day of your surgery. However, you’ll need someone who can drive you home and stay with you overnight. Having a general anaesthetic can really take it out of you. You might find that you're not so co-ordinated or that it's difficult to think clearly. This should pass within 24 hours. In the meantime, don't drive, drink alcohol, operate machinery or make any important decisions.

Before you go home, you’ll be given some advice about caring for your wounds, signs of infection to look out for and pain relief you can take. You’ll also be told what the arrangements are for follow-up in the clinic.

Recovering from anal fistula surgery

You’re likely to have some discomfort for the first week or so after having anal fistula surgery. You can take over-the-counter painkillers such as paracetamol or ibuprofen if you need pain relief. Constipation can be common after surgery. Your surgeon may recommend that you take a laxative to soften your stools and help to reduce any discomfort. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

Your wound should heal within six weeks. You might find it helpful to use a gauze pad in your underwear to protect your clothes from any discharge from your wound.

Have a bath or shower two or three times a day to help ease pain and discomfort as well as keeping your wound clean. Dry the area carefully afterwards. Don’t add anything to the bath water as this can irritate your wound.

Your surgeon will give you advice about driving, going back to work, having sex and getting back to your usual activities and routine.

Complications of anal fistula surgery

Complications are when problems occur during or after the operation. The possible complications of any operation include things like infection, bleeding or an unexpected reaction to the anaesthetic. Specific complications of anal fistula operation include the following.

  • Losing bowel control. This means you can’t control when you poo or sometimes just when you pass wind. The risk of this happening is different for different types of procedure. When your surgeon assesses you before your surgery, they’ll advise which type of operation is best to minimise the risk of this happening.
  • Your wound takes longer than usual to heal.
  • The fistula may come back. The chance of this happening varies between different procedures. You may need a different type of operation if it comes back.
  • Narrowing (stenosis) of your anal canal – the end of your back passage. This can happen as your fistula starts to heal, and can make it difficult to pass faeces (poo). Your doctor may prescribe medicines to help with this.

Frequently asked questions

  • An anal fissure is a tear or an ulcer that develops in the lining of your anus. There is usually no obvious cause of an anal fissure, though sometimes passing a hard stool can cause one to develop. The treatment for a fissure is to keep the area clean, take painkillers and make sure that your stools are soft and easy to pass. This means drinking enough fluid and eating fruit, vegetables and foods that have fibre in them. Doing this gives the fissure a chance to heal without other treatment.

    An anal fistula is a tunnel that connects the skin near your anus to your rectum. It usually develops after an infection. Treatment for anal fistula involves having an operation.

    If you have any symptoms affecting your back passage, such as pain or bleeding from your bottom, it’s important to seek advice from your GP.

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  • Reviewed by Pippa Coulter, Freelance Health Editor, October 2019
    Expert reviewer Mrs Sara Badvie, Consultant Laparoscopic, Colorectal and General Surgeon
    Next review due October 2022